A growing number of factories and residences are installing solar power devices. Electrical appliances in the factory or the home may consume the energy generated by a solar power device with the remaining surplus energy sold back to the power company. This kind of solar power device requires a power control device that controls the supply of the energy generated by the solar power device.
While the power control device may supply the surplus energy to the power company's power grid, the surplus energy cannot be supplied to the grid, i.e., sold back to the power company when the voltage setting of the grid exceeds a certain value (set point) the surplus energy cannot be supplied to the grid. In this case, some or all the surplus energy is not used, but cannot be sold back to the grid, i.e., this creates potential usable energy.
Consequently, techniques for making this potential usable energy available have been disclosed. For instance, Patent Document 1 describes a power control device that terminates supply of surplus energy to the grid when the voltage setting of the grid exceeds a threshold, and modifying the operation of an electrical appliance so that the appliance consumes more power. Patent Document 2 also describes a power control device; the device controls supply to the grid and the charging and discharging of a battery to thereby ensure that the voltage setting of the grid remains at or below a predetermined threshold.